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Old 10-30-2011, 10:17 AM
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DIY Simple Active Preamp

I was looking into making a simple preamp I considered the Pass B1 Buffer but was worried if it would have enough gain.

I decided to make one out of parts I had and make it as simple as possible.

I used a pretty standard design which I found on Rod Elliot's site, I simplified it greatly so now it has few parts and only one film cap in it, the opamp I used is a AD823.



I etched a PCB and assembled it and tested it out, surprisingly it worked first time. It has too much gain, I am going to change out the 100k resistor in the feedback loop to a lower value which should take care of that.

I hooked it up between my phono stage and the main amp inputs of my Yamaha CR-1020 and then did a comparison with the Yammy using it's preamp. The bass is much more extended for a start the sound being more full bodied and open it should improve once it burns in as I used a 2.2uf Panasonic ECW-F polypropylene which may open more up after some hours.

Initially it sounds much better than the pre in the Yamaha, the acid test is going to be when I try it in my main setup and put it up against my Yamaha C4 but the way it sounds now it might just be better.
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Last edited by HypnoToad; 10-30-2011 at 03:13 PM.
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Old 10-30-2011, 10:37 AM
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You knew that was coming....
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Old 10-30-2011, 11:09 AM
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Quote:
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You knew that was coming....
Don't laugh I just threw it together to see if it worked.

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Old 10-30-2011, 11:23 AM
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Old 10-30-2011, 07:57 PM
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After some adjustments I still have plenty of gain and listening to Grover Washington Jr - Strawberry Moon and my bedroom system has never sounded so good. With a little burn in time it got a whole lot better.

More air around the instruments and bass to die for, I am thinking of putting one in a case with a 3 input switch including the phono stage so it can run off the same batteries using decent components, my volume control is a ratshack one. Simple seems to better.

But the sound is amazing a huge jump from the internal Yamaha preamp, still haven't tried it against my C4 but I am pretty sure of the result already.

You can build one of these really cheaply.
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Last edited by HypnoToad; 10-30-2011 at 08:05 PM.
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Old 10-30-2011, 09:20 PM
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very cool
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Old 10-30-2011, 09:27 PM
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This is great! You have to give this a name! I'm gonna try it, though I'll use point to point wiring cuz I've never etched a board. I have the ESP P05 board that I could use instead of 9V batteries..
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Old 10-30-2011, 09:45 PM
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It's the Simple Preamp or SP.

I changed a few things, I put in 51k resistors instead of the 100k in the feedback loop and changed out the 1.5k for some 27k in the input. I would also use a 250k pot instead of the 100k as it builds up volume very quickly. I am going to try one as soon as I get on to a decent one reasonably priced. You could also try a nice axial 2.2uf cap as well, although for the money the Panasonic's are very good.

I also put some polar 47uf caps from the op amp supply rails to ground with some 0.1uf bypass caps on them for stability and low noise.
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Old 10-30-2011, 10:12 PM
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I did not realize that a pre-amp could be done so simply. Very interesting. I agree that simple is better. I prefer not to have tone controls, multiple inputs, etc. I have never DIY'd anything but this project has got me thinking In post #1 you mentioned that you simplified the base design, in what ways did you simplify?

What software do you use to make the schematic?
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Old 10-30-2011, 10:43 PM
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Cool project. Bonus point on the minimalism. I have a class-A power buffer amp project with the same general vision. I should kickstart it this fall/winter; been sitting on shelves for some time despite having most parts.

All you need is a good enclosure and it will look as good as it sounds!

az
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Old 10-31-2011, 04:35 AM
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Hey Toad, wanna do a group board offer???

Cheers,

Bob
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Old 10-31-2011, 09:46 AM
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Quote:
Originally Posted by roger2 View Post
I did not realize that a pre-amp could be done so simply. Very interesting. I agree that simple is better. I prefer not to have tone controls, multiple inputs, etc. I have never DIY'd anything but this project has got me thinking In post #1 you mentioned that you simplified the base design, in what ways did you simplify?

What software do you use to make the schematic?
I use ExpressPCB and ExpressSch. I usually just make the design in ExpressPCB as I can print it out for etching, I wouldn't use it for a commercial board as not many companies accept the files.

I removed the balance control and took out some other parts in the output, it resembles the output stage of the CNC now. I just wanted something simple to see if it would work, I measured the outputs and there is no DC. It's virtually just a low gain stage with a volume control at the front.

You can add different inputs if you like.

I am still not sure about the volume control as it is very sensitive. If anyone has any ideas about implementing it better let me know.
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Old 10-31-2011, 01:49 PM
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Quote:
Originally Posted by HypnoToad View Post
I am still not sure about the volume control as it is very sensitive. If anyone has any ideas about implementing it better let me know.
Maybe use Rod's log faking circuit with a linear pot?
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Old 10-31-2011, 02:44 PM
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search J-fet BOZ, (Bride of Zen) over on DIY... nice, gain, very simple...

Russellc
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Old 10-31-2011, 04:46 PM
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Aside from an abundance of caution, there's really no reason to use an output DC-blocking cap in op-amp circuits with such low gain. You could eliminate that item unless you expect to be using op-amps with substantial input offset voltage. Even in that case, you might be better off with an offset trimmer.
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